Conventional treadmills provide a platform with a moving belt on which a user can walk or run in place. Most conventional treadmills have a motor that drives the belt over the platform. Some conventional treadmills are motorless, but have the platform set at a fixed angle or slope so that with each step the user's weight pushes the belt down along the platform. A flywheel may be coupled to the belt to maintain the belt motion that is generated by the user with each step.
Conventional stair climbing exercise machines (also called steppers) generally have two pedals that a user alternately steps against to simulate stair climbing. Devices that combine the stair climbing aspect of steppers with the moving belt of a treadmill have also been developed. For example, U.S. Pat. No. 7,097,593, assigned to Nautilus, Inc., discloses a combination treadmill/stepper. Like conventional treadmills, however, conventional combination treadmill/steppers, such as the device disclosed in U.S. Pat. No. 7,097,593, are motor-driven so that the speed of the moving belts and/or the stepping action can be more accurately controlled.